Cellulose triacetate coating compositions



62 per cent.

Patent ed Jan. 23, 1945 CELLULOSE TRIACETATE COAIIIN COMPOSITIONSCharles Begin, Terre Haute, Ind.,- assignor ,to Commercial SolventsCorporation, Terre Haute, Ind., a corporation of Maryland 'No Drawing.Application April 22, 1942, Serial No. 440,099

7 Claims. (01. 106-176) The present invention relates to new andimproved cellulose ester coating compositions. More particularly, it isconcerned with a method of producing cellulose triacetate coatingcompositions capable of forming stable, clear, tough, andwater-resistant films.

Cellulose acetate is produced commercially in a number of grades, whichdiffer in their degree of acetylation. In the ordinary processes bywhich cellulose acetate is manufactured, it is first produced as ahighly-esterified product possessing an acetic acid content ofapproximately This material, however, is soluble only in a very limitednumber of solvents, such as tetrachloroethane, ethylene dichloride, etc,and because of the relatively high toxicity of the latter solvents,solutions of highly acetylated cellulose acetate are obviouslyimpractical for most which exhibits greater water resistance than isexhibited by the lower acetylated cellulose acetate films. As possiblesubstitutes there have i been proposed coating compositions in' whichthe secondary acetates have been replaced by cellulose acetate butyrate,o'r cellulose acetate propionate. These materials in general, however,

, give films which are substantially softer than acetate coatingcompositions have previously coimnercial applications. The commercialgrades hydroxyl groups. Because of the introduction of hydroxyl groupsinto the cellulose acetate, the

solubility of the latter is considerably increased and it may readily bedissolved in a number of the oxygenated organic solvents, such asacetone,

methyl acetate, ethyl lactate, diacetone alcohol, mixtures ofnitroparamns and alcohols. and the like.

The films formed from such cellulose acetate solutions possess certaindisadvantages, however,

which tend to prevent the use of considerable quantities thereof in manyfields. For example, such films possess rather poor water-resistantproperties, and if immersed in water, or even expossessed by filmsformed. from the various secondary grades of cellulose acetate, therehas be n an existing need for a film-formin material having essentiallythe same solubility characteristics been prepared by using as a solventa mixture consisting of approximately per cent nitromethane and 30 percent of an aliphatic alcohol having less than five carbon atoms, ormixture in which approximatelyhalf oi the alcohol content is replacedby. an aromatic hydrocarbon, such as benzene, or toluene. Such solventmixtures will dissolve .cellulose triacetate satisfactorily, and theresulting solutions thus produced are in most instances perfectly clear.I have found it impossible for all practical purposes, however, toproduce clear films by the use o such nitromethane-alcohol mixturessince the range of nitromethane-alcohol proportions permissible from thestandpoint of solubility is very narrow, and inasmuch 'as'these' twovolatile liquids do not evaporate at the same rate, the necessarysolvent balance is rapidly destroyed during the drying of the film,leading to a precipitation of the cellulose triacetate.

I have now discovered that the nitroparafiins,

sible to prepare cellulose triacetate solutions, posses'sing anexceedingly high tolerance for a. wide,

variety of solventmixtures, and which may contain the highernitroparafflns, as well as nitromethane. It is therefore obvious thatsuch compositions, particularly from the standpoint of as the secondarygrades of cellulose acetate, but 55 commercial application, are muchmore desirable I tures, since the latter, as mentioned above, aresubject to the disadvantage that the permissible very rapidly when theconcentration of l-nitropropane falls below 30 per cent.

In the case of solutions of cellulose triacetate prepared by dissolvingthe latter in tetrachloroproportions of nitromethane and alcohol, whichethane or in a mixture of 90 parts of ethylene may be utilized incellulose triacetate solutions. chloride and 'parts of anhydrous ethylalcohol, are restricted toavery narrow range. it will be noted that thetolerances for l-nitro- As a further result of the present invention,propane and for mixtures of l-nitropropane and the quantity of truesolvent required in the prepethyl alcohol are high, while the tolerancesfor aration of cellulose triacetate solution has been It) ethyl alcohol,butyl alcohol, butyl acetate, and

materially decreased. Such an improvement contoluene are very low.stitutes a distinct advance in the art of cellu- The tolerances of asolution of cellulose triacelose triacetate coating compositions in viewof tate in a mixture consisting of '70 per cent nitrothe fact that theknown true solvents for cellumethane and 30 per cent anhydrous ethylalcolose triacetate are comparatively toxic substances. s hol, areobservedto be very high for l-nitropro- Consequently, th'isproperty hasgreatly hindered pane or its mixtures with alcohols. The nitrothe wideindustrial application of cellulose triacemethane-alcohol mixtures canthus be modified tate solutions in many fields for which they weregreatly by other liquids, and can also impart otherwise admirablysuited. Furthermore, solusolvent power to the lnitropropane. tions ofcellulose triacetate dissolved in true 501- go As previously stated, thehigh toxicity of the ventsof the aforesaid type have a very lowtolertrue or active solvents for cellulose triacetate tune for all ofthemore common volatile organic make it desirable to employ such materialsin liquids, suoh as esters, ketones, alcohols, etc., as minimumproportions and the factor which deshowninthe table appearing below.termines'this minimum value is the degree of These data, likewise showthe comparatively solubility of the cellulose triacetate in the parhightolerances of solutions of cellulose triacetate ticular solvent mixturecontemplated. when in various true solvents therefor, for certain ofemploying cellulose triacetate in the preparathe nitroparafllns, 'aswell as for mixtures of the tion of coating compositions, I have foundit nitroparafllns with toluene and/or alcohols. desirable to dissolve itfirst in the form of a Table Composition of cellulose trlacetatesolution Diluent or diluent mixture Tolerance l-nitro opane More than10. 0 l-nitropro e 3.9 gal grlilliity grpggs etlyl alcohol. anhydrousethyl aleohoL More than 10.0 3092 l-nllxopropane 30$ dr More than 15.0toluene I 20% 1 nitropropane 2m solution cranium iriacetata (00.9%acetic acid) in tetrachloroathana @87 gggz fiffff j ff I 20%l-nitropropane- 2 0 o. @3110] 39%; t 'g More than 15. 0 1.. lihydmfittinaara; 40% Z-nitropropsne 4A my, bntanol Ethyl acetate--- 1 gButylaoetata 0.1 Ethyl alcohol 95%)-- 4 Ethyl alcohol (auhyd)-. 5%lolutknolcelluloso mm 02% acetic acid) lntetrachlorosthsno. E3 1,3522: 1.I n (1.5 01 0.6 bultyl aaatfite- 1.2 v 1. a an More than 7.0 a I mmwwmmorethan8.0 solution i (00.9% acetic acid) in 90-10 ethylene chloridemqthyl 3 Butyl acetate g More than uol Anhydrous cthylslcoh 0.5lbrhsgllntlcdl lmtielcid) in-30nitromcthsno-anhydrous .H' ggwtt More mm7. 5

I -i ""'"'.I

llhfit tttl ma--..--} 7 5 In the above table the of the solutionproducedi'rom tetrachloroethane and cellulose triacetate for thethree-component mixtures 01' l-nitropropane, alcohols, and toluene, aresubstantlally higher than'the values for the simple mixtures oi"l-nitropropane and alcohols free from toluene. The results obtained alsoindicate that the tolerance of tetrachloroethane for mixtures ofl-nitropropane andalooholsdecreases 2,868,062 aration of the more dilutesolutions. Since the' thinners employed need not contain any of thetoxic true solvents, this practice allows the formulation of finalsolvent mixtures containing a minimum of said true solvents. In thisconnection the process oi solution is aided considerably by elevatedtemperatures. For example,.'I, have observed that it 'a well-dispersedmixture of cellulose triacetate and volatile solvents is sub-' jected toa temperature of about 70 C. for a relatively short period, .e.. g.,'one-half hour, the process of solution is improved appreciably. As aresult, stock solutions prepared under such conditions may contain fromto aboutl5 per cent less of the true solvent than is necessary to obtaincellulose triacetate solutions of equal nitropropane and to per centethyl alcoho]. Such solvent mixtures can be readily, di-

luted with thinners containing no tetrachloroethane whatever. The finalcellulose triacetate solutions thus obtained will therefore contain thetrue solvent, in this case tetrachloroethane, in about one-third theamount present in the stock solution, 1. e., 7 to 8 per cent. Thus, itmay.

be seen that the cellulose triacetate solutions of the present inventionare considerably less ob- ,iectionable than those of the" prior art fromthe standpoint of toxicity. 1

Frequently, concentrated solutions of cellulose triacetate containingnitroparafiins, tend to in-' crease in viscosity and gel on aging. Thisparticular type of instability has been found to be directly connectedwith the richness of the s vent mixtures, Such solutions of cellulosetriacetate which contain only moderate proportions of aromatichydrocarbon-alcohol mixtures, are, however, found to be fully stable tostorage. In the actual preparation and handling of such solutions, itwill therefore be advisable to employ moderate amounts of said aromatichydrocarbon-alcohol mixtures in the concentrated stock bases whichconsist essentially of cellulose triacetate and a true solvent therefor.Additional quantities of the aromatic hydrocarbonalcohol mixture may beconveniently introduced into the diluent mixture. Any of the customaryaromatic hydrocarbons commonly employed in rapid evaporating solvent,such as ethylene chloride, is utilized as the true solvent. Theproportion oi such solvents will also be found to depend upon thecharacter of the nitroparaflin mixture, greater proportions beingnecessary in the case of solvent mixtures containing relatively largepercentages of comparatively slow evaporating solvents, such as butylalcohol, butyl acetate, etc. .The proportion of true sol-. ventsnecessary will also depend somewhat on the nature of the cellulosetriacetate used, i. e.,

the substantially completely-acetylated cellulose triacetate whichcontains approximately 62 1 nitroparafllns utilized will likewise befound to ponents of the solvent mixture. isfactory solutions may beprepared by employing solvent mixtures containing from 20 to40 perpercent acetic acid, or the slightly hydrolyzed grade having an aceticacid content of from 59 to 60 per cent." However, in general a number ofsolvent mixtures containing as little as from 3 to 5 per cent of one ormore of the abovementioned true cellulose triacetate solvents, will befound to be satisfactory for the production of cellulose triacetatesolutions capable of forming clear, tough, and water-resistant films.

The nitropa-raflins, in addition to nitromethane, which may be employed,are nitroethane, 1-nitropropane, 2-nitropropane, the nitrobutanes, thenitropentanes, and the like. The quantity of vary with the character ofthe true solvents employed, well as the acetic acid content of thecellulose triacetate. In general, however, the nitroparaflln content ofthe solvent mixture may vary from approximately 30 per cent to 70 percent.

The alcohols used in preparing the cellulose triacetate compositions ofthe present invention may be any of the lower saturated aliphaticmonohydric alcohols, and particularly those containing 1 to .4 carbonatoms. such alcohols utilized is, of course, subject to variation,depending upon the particular grade of cellulose triacetate, the alcoholemployed, and the character and quantity of the other com- 10 to 30 percent of the solvent mixture.

My invention may be further illustrated by th following examples whichdescribe typical comcoating compositions, may be utilized for thispurpose, such as, for example, benzene, toluene and xylene. I prefer,however, to employv toluene for most purposes.

Examples of the true 'or active solvents which may be utilized in theformulation of cellulose triacetate compositions possessing theaforesaid properties, are tetrachloroethane, trichloroethane. ethylenechlorohydrin, dioxane, and a whether a slow evaporating solvent, suchas,

tetrachloroethane, is employed, or a relatively positions that may beproduced in accordance with my discovery.

" Example I Cellulose triacetate having an acetic acid content of 61.0per cent was added in a ratio of 15 grams per c. c. of a solvent mixtureconsisting f 24 parts tetrachloroethane, 50 parts 1.-nitropropane and 26parts ethyl alcohol. To the resulting solution was added, with thoroughagitation, a thinner consisting of 70 parts l-nitropropane, 19 partsethyl alcohol, 30 parts butyl alcohol and 81 parts toluene. Thissolution, when applied in accordance with any of the common methods ofapplication, produced a clear, tough .and water-resistant film.

I Example vI I Tov a solvent-mixture consisting of 25 parts dioxane, 48parts l-nitropropane and 27 parts ethyl alcohol, cellulose triacetatehaving an acetic The proportion of In general, satacid content of 59 percent, was added in a ratio of grams of cellulose triacetate per 100 c.c.

' of solvent. The resulting solution was slightly cloudy; however, withthe aid of heat and agitation it became perfectly clear. A thinnerconsisting of 100 parts l-nitropropane, 32.5 parts butyl alcohol, 62.5parts toluene and 30 parts ethyl alcohol was then added thereto withagitation. The composition thus secured, when aptrue solvent for saidcellulose triacetate selected from the group consisting oftetrachloroethane, trichloroethane, ethylene chloride, ethylenechlorohydrin, and dioxane, such solvent mixture being substantiallynon-toxic and easily capable of maintaining the cellulose triacetate ina dissolved state throughout the drying process when said composition isapplied to a smooth surface.

2. A composition of matter comprising cellulose triacetate having anacetic acid content of from about 58 per cent to about 62 per centdissolved in a solvent mixture comprising a major proportion of anon-solvent mixture containing a lower nitroparaffin, a lower aliphaticalcohol, and an aromatic hydrocarbon, and a minor PTO-e portion of atrue solvent for said cellulose triacetate selected from the groupconsisting of tetrachloroethane, trichloroethane, ethylene chloride,ethylene chlorohydrin and dioxane, such solvent mixture beingsubstantially nontoxic and easily capable of maintaining the cellulosetriacetate in a. dissolved state throughout the drying process when saidcomposition is applied to a smooth surface.

3. The composition of claim 2 in which the aromatic hydrocarbon istoluene.

4. A composition of matter comprising cellulose triacetate dissolved ina solvent mixture comprising a major proportion of anon-solvent mixturecontaining nitromethane and a lower aliphatic alcohol, the predominantportion of said non-solvent mixture consisting of said nitromethane, anda minor proportion of a true solvent for said cellulose triacetateselected from the group consisting of tetrachloroethane,trichloroethane, ethylene chloride, ethylene chlorohydrin, and dioxane,such solvent mixture being substantially non-toxic and easily capable ofmaintaining thecellulose triacetate in a dissolved state throughout thedrying process when said composition 5 applied to a smooth surface.

5. A composition of matter comprising cellulose triacetate dissolved ina solvent mixture comprising a major proportion of a non-solvent mixturecontaining l-nitropropane and a lower aliphatic alcohol, the predominantportion oi said non-solvent mixture consisting of said l-nitropropane,and a minor proportion of a true solvent for said cellulose triacetateselected from the group consisting of tetrachloroethane,trichloroethane, ethylene chloride, ethylene chlorohydrin, and dioxane,such solvent mixture being substantially non-toxic and easily capable ofmaintaining the cellulose triacetate in a dissolved state throughout thedrying process when said composition is applied to a smooth surface.

6. A composition of matter comprising cellulose triacetate having anacetic acid content of from about 58 per cent to about 62 per centdissolved in a solvent mixture comprising a major proportion of anon-solvent mixture containing nitromethane, a lower aliphatic alcohol,and an aromatic hydrocarbon, the predominant portion of said non-solventmixture consisting of nitromethane, and a minor proportion of a truesolvent for cellulose triacetate selected from the group consisting oftetrachloroethane, trichloroethane, ethylene chloride, ethylenechlorohydrin,

CHARLES BOGIN.

